Wash the spinach well and remove the ends of the stems. Dice the onion and place in a large pan over medium heat and sauté in a little water. The bottom of the pan should never get dry. Gradually add the spinach to the pan, season with pepper and chilli and cover with a lid. Cut the tomatoes into 1 cm cubes and add to the pan. Now let everything simmer gently for 8-10 minutes with the lid closed.
Turn off the heat and stir the peanut butter into the brew. Possibly add a dash of water or stir in a little more peanut butter until the sauce has the desired consistency. Season if necessary.